The present invention relates to sound transducers and in particular to an inertial microphone/receiver device.
In the conventional microphone air, disturbed by soundwaves, serves to move a diaphragm which in turn serves to disturb an electro-magnetic field to thereby generate an electrical signal. In the conventional receiver the reverse occurs. That is, an electric current serves to disturb an electro-magnetic field to in turn drive a diaphragm to generate sound waves. While such transducers have many benefits including excellent frequency response, their principal shortcoming is that they can only be used in an environment where air is available as a driving (or driven) medium. Another shortcoming is that they cannot readily differentiate between sources of moving air and hence, particularly as a microphone, they are extremely noise sensitive. As a result they cannot readily be utilized in certain extreme environments, such as where there is a high level of ambient noise (e.g. near motorcycles, heavy equipment, etc.) or where for one reason or another a speaker's mouth is masked (e.g. surgical theaters, fire fighters with gas masks, etc.).
To overcome the shortcomings of the conventional air driven transducer it has heretofore been suggested to utilize inertial transducers. In an inertial microphone the vibrations of a sound source are applied to a relatively low mass connected to a relatively large mass through a spring diaphragm. The movement of the low mass with respect to the large mass causes the spring diaphragm to oscillate within an electro-magnetic field thereby generating an electric signal. In operation as a speaker the electric signal is used to vary an electro-magnetic field to thereby drive a spring diaphragm connecting a large mass to a small mass thereby causing the one mass to oscillate with respect to the other to produce sound waves. Since such transducers need not rely on air movement they can be utilized in bone conduction microphones and receivers.
Heretofore the principal problem of inertial transducers has been that they are extremely frequency limited and hence produce an unnatural sound particularly when used for voice communication. The reason for this is that the spring diaphragm is basically a single frequency device so that all signals tend to peak at the natural frequency of the spring. This produces an extremely degraded and distorted signal for voice communication.
In view of the above, it is the principal object of the present invention to provide an improved inertial transducer having a relatively flat response over a relatively wide frequency range.
Another object is to provide such a transducer in which the range in which the frequency response is generally flat corresponds with the principal frequencies of voice communication.
Still another object is to provide such a transducer in a size and shape that may readily be adapted for a microphone or ear speaker.
A further object is to provide such a transducer in a form that is realtively simple and economic to assemble.
Still other objects and advantages will be apparent from the following description of the invention.